The invention relates generally to diaphragm pumping devices, and particularly to improvements to such devices for enhancing pumping capability and for reducing diaphragm wear and breakage problems. Diaphragm pumps represent an extremely efficient approach to pumping liquids through the use of reciprocating flexible membrane which may be used to expand and contract a liquid pumping chamber having suitable input and output control valves. The most significant problem associated with such diaphragm pumps is the problem of protecting the diaphragm membrane from breakage. In the idealized situation the flexible diaphragm, made from rubber or plastic material, is interposed between two fluid-filled chambers. The chamber on one side of the diaphragm is filled with hydraulic oil and the chamber on the other side of the diaphragm is filled with the liquid to be pumped, such as water, paint, or other fairly low viscosity fluid. The oil-filled chamber is alternately pressurized and relieved and the pumping chamber is correspondingly filled and emptied through suitable control valves, to deliver pumped liquid at elevated pressures. The pressure forces across the diaphragm are, to the highest extent possible, kept in equilibrium so that the diaphragm itself experiences very little pressure gradient. This enables a diaphragm, which itself has high resiliency and poor capability of withstanding differential pressures over several pounds per square inch (p.s.i.), to be able to deliver fluid pressures upwards of several thousand p.s.i. Therefore, the design goals which must be achieved in proper diaphragm pump construction require that pressure stresses across the diaphragm be minimized at all times during the reciprocating stroke of the diaphragm.
Yet another problem which must be considered in the proper design of a diaphragm pump is the control of the diaphragm mean deflection position. In an idealized situation the diaphragm deflects forward and backward an amount equal to the stroke of the driving piston, and this deflection is from a "rest" position usually determined by the circumferential line where the diaphragm edge is fastened to the pump structure. To the extent that the hydraulic oil volume in the enclosed chamber, bounded by the driving piston on one end and the diaphragm on the other end, can be kept at a constant "ideal" volume, the diaphragm deflection will always occur between the same forward and backward positions. In an actual situation the fluid volume in the oil filled chamber can accumulate beyond the "ideal" volume and thereby cause the diaphragm to deflect about a mean position which shifts from its intermediate "rest" position. As this mean deflection position shifts it causes increased stress on the diaphragm, because the edge of the diaphragm remains fastened to the pump structure along its circumferential line but the maximum deflection distance moves farther from this line. If uncontrolled, this effect will ultimately cause the diaphragm to rupture.
Attempts at minimizing forces across the diaphragm in the prior art have always manifested themselves in valve controls in each of the two reciprocating stroke directions. Techniques and apparatus have been devised for relieving excess oil pressure during the pressure stroke and in replenishing deficient oil volume during the return stroke, or alternatively unloading and relieving pumped liquid pressure.
Another problem which has been dealt with in the prior art is the apparatus for reciprocating a diaphragm. A large number of piston-operated reciprocating devices have been introduced into the art, which have been driven by crank assemblies, wobble plates, cams, and other reciprocating motion drive sources. The inventors herein have found the conventional crank shaft to give the most preferred driving operation for this type of pump, particularly when used in conjunction with the apparatus disclosed herein.